Let me admit that my perception implied by the question may be wrong. (Aptitude may be more popular by users than APT; unfortunately, I did not find robust data about usage.) But, wherever I see, let's say, official documentation, manpages, installation instructions, tutorials and videos, I mostly see the mention of APT. Aptitude, on the other hand, has very few mentions.
When I tried to see some technical comparisons, I almost always came across the argument that Aptitude is better than APT. Its dependency resolver is more robust than APT and it represents information in beautiful way. APT lacks some of these features.
Even if it has these plus points, Aptitude is not shipped by default on any Debian/Ubuntu based distros, and is not mentioned anywhere either. Also, whatever technical comparisons and mentions of Aptitude I found on the Internet are very old. (Almost 6 to 10 years old!) It seems that very very few people advocate Aptitude nowadays.
So my question is, why are more and more people are endorsing and promoting APT and not Aptitude? What are some technical constraints of Aptitude? In the end, distribution vendors may have some genuine reasons for this thing.
Does anyone know?